1. Field of the Invention
This invention relates in general to subsea well drilling, and in particular to a means for collecting cuttings produced while drilling the well for a first string of casing after conductor pipe has been installed.
2. Description of the Prior Art
When drilling with a floating drilling vessel, normally a guide base will be installed on the sea floor. Then the well will be drilled or jetted to an initial depth of typically around 300 feet. Large diameter conductor pipe, normally 30 inches in diameter, will be installed in this initial portion of the well. An outer wellhead housing secures to the upper end of the conductor pipe and locates at the subsea floor on the guide base.
Then, the operator lowers a drill bit through the outer wellhead housing and drills through the conductor pipe to a depth that may be around 1,000 feet. The operator then runs a first string of casing, which is normally 20 inches in diameter. An inner or high pressure wellhead housing locates at the upper end of the 20 inch casing. The inner wellhead housing lands in the outer wellhead housing. The operator cements the 20 inch casing in place.
The operator installs a riser to the exterior of the inner wellhead housing leading to the surface. A blowout preventer stack is connected into the riser at a subsea location. The operator will then drill the well for at least two additional strings of casing.
While drilling the well for the 20 inch casing, there normally will be no riser to the surface because the riser will connect to the inner wellhead housing, which has not yet been installed. As a result, cuttings produced during drilling for the 20 inch casing flow up over the outer wellhead housing and pile up on the guide base. Sometimes the pile of cuttings can be a problem. The extent of the cuttings may result in the operator having to extend the outer wellhead housing higher above the sea floor than desired.
Proposals have been made to return cuttings to the surface. These proposals involve various techniques to utilize a riser while drilling the 20 inch. While this would prevent the build up of cuttings around the outer wellhead housing, the proposals necessitate the use of wellhead structure that will be other than of the type conventionally employed.